Speech transmission system



May 12, 1942. s. R. TAYLOR SPEECH TRANSMISSION SYSTEM Filed Feb} 25, 1941 a Sheets-Sheet 1 khan lNl ENTOR By 5/2 TAYLOR ATTORNEY May 12, 1942. R, T LOR 2,282,437

SPEECH TRANSMISSION SYSTEM Filed Feb. 25, 1941 3 Sheets-Sheet 3 I I k l- I l l 3 g g ro PHANTOM REPEA rm WEST INVEN 70/? E. 1?. T4 FL 0/? A T TORNEV Patented May 12, 1942 iJNi'rEo STATES PATENT or fice SPEECH TRANSMIS SION SYSTEM Edmund R. Taylor, Mount Vernon, N. Y., assignor to Bell Telephone Laboratories,Incorporated. New York, N. Y., a corporation of New York Application February 25, ian'seriai No. 380,461

(0.1. its-+3).

9 Claims.

This invention relates to a speech transmission system of the type which includes telephone repeaters spaced at intervals along the transmission line and more particularly to such a system adapted to transmit, in addition to the speech currents, direct current signaling current.

An object of the invention is to increase the emciency of speech transmission systems.

A more specific object of the invention is to prevent pulse distortion due to cross-fire resulting from application of direct current signaling current to the speech transmission lines.

A copending application in the name of applicant and another (P. G. Edwards) Serial No. 380,446, filed Feb. 25, 1941, entitled Speech transmission system, discloses, among other things, a novel way of applying direct current signaling currents to a speech transmission system and a novel arrangement for by-passing such signaling currents around intervening telephone repeaters. Briefly stated here, but described in detail in the copending application referred to, the telegraph direct current signaling currents are applied to the voice transmission lines in shunt with capacitances located between the line windings of the line repeating coil whereby the direct current composite sets are shunted by a low impedance at voice frequencies and the by-pass circuits are connected to the speech transmission lines in a similar manner. The arrangement contemplated by the present invention is particularly applicable to the above arrangements as fully disclosed by the copending application referred to.

A feature of the present invention is means, adaptable alike to the composite set connection i A further feature of the present invention is 1 adjustable means for varying the coupling between coils utilized in the neutralizing means in order to attain a more exact corrective factor.

In accordance with a specific embodiment of the invention a neutralizing or bucking inductance is provided in each leg of the direct current composite set in series with the respective retardation coils of the composite set. Signaling currents passing through either leg of the composite set will give rise through induction to current in the inductance of the other composite leg; this induced current is utilized to neutralize any disturbing current set up in the secondary pfthefline repeating coil by-pass'ageof the Signaling currents referred to. Coupling between the two inductances is varied by means of a closed loop circuit comprising a third inductance and a variable resistance.

A complete understanding of the various novel arrangements contemplated by the present invention as well as appreciation of the various desirable features thereof will be gained by consideration of the following detailed description in connection with the annexed drawings in which:

Fig. 1 illustrates schematically a speech transmission system of the type utilizing line repeating coils and including cross-fire preventing means which embodies features of the present invention;

Fig. 2 illustrates schematically one terminal of a speech transmission system of the type utilizing combined lineand hybrid coils and including cross-fire preventing means which embodies features of the present invention; and

Fig. 3 illustrates'schematically a portion of the system of Fig. 1 modified to include crossfire preventing means in the repeaterby-pass. Referring now to Fig. 1 there is illustrated schematically a speech transmission system including a west terminal, an intermediate repeater section and an east terminal. It will. be understood that there may be, and in most cases will be, more than one. intermediate repeater provided between the terminals.

Voice frequency currents produced by transmitting apparatus associated with terminal lines H and 12 of side circuit No. 1 are applied to lines 13 and [4 through repeating coil [5. These speech currents pass over lines it and it to the intermediate repeater section where they are impressed on linesection, W by repeatingcoil i1. One-half of the speech energy impressed on line section I6 passes through inductive coupling into output path 2| of east-west amplifier 22 and is lost; the useful half of the speech energy passes directly into input path 23 of west-east amplifier 24 and is amplified. v v v The amplified speech energy now present in west-east amplifier output path 25 is impressed on line section 26 where it again divides, onehalf being absorbed by balancing network 2-1 east amplifier 24 so'that none of this energy from east to west is accomplished in a manner similar to that described above as is transmission of voice frequency currents over side circuit No. 2 from west to east and from east to west.

Voice frequency currents produced by the voice frequency apparatus associated with lines and 52 of the west phantom terminal are impressed through repeating coil 53 on the phantom circuit which is derived over lines 54 and 55. Line 54 terminates in side circuit No. 1 between capacitances 56 and 51 which, in turn, are connected in series with line windings II and 12 of repeating coil I5 while line 55 terminates in side circuit No. 2 between capacitances I3 and I4 which, in turn, are connected in series with line windings I5 and 16 of repeating coil 17.

Upon reaching the intermediate repeater secton, the phantom voice frequency currents are picked off over lines 8I and 82 and impressed by repeating coil 83 on the phantom intermediate repeater section. After amplification by phantom west-east amplifier 84 (in a manner similar to that described above in connection with transmission of speech currents over side circuit No. 1) the amplified currents are impressed on lines 85 and 86 by repeating coil 81 and returned thereover to the phantom circuit for transmission to the east terminal.

Upon reaching the east terminal, the phantom voice frequency currents are picked off over lines IN and I02 and impressed by repeating coil I03 on phantom terminal lines I04 and I05 over which they are transmitted to the voice frequency receiving apparatus. associated with the east phantom terminal.

- It will be understood that transmission of voice frequency currents over the phantom circuit from east to west is accomplished in a manner similar to that described above.

Direct current signals, for example telegraph signals, are impressed on line I3 at the west terminal through retardation coil I II and bucking coil H2 which are connected in series with repeating coil line winding II and are impressed on line I4 through retardation coil H3 and bucking coil H4 which are connected in series with repeating coil line winding I2.

At the intermediate repeater section these direct current signals are by-passed around the amplifiers over a by-path which comprises retardation coils H5 and H6 and line III and retardation coils I3I and I32 and line I33. Upon reaching the east terminals the direct current signals are transmitted to the direct current receiving apparatus associated with the east terminal through bucking coil I34 and retardation coil I35 which are connected in series with repeating coil line winding I36 and through bucking coil I31 and retardation coil I4I which are connected in series with repeating coil line winding I42.

It will be understood that transmission of direct current signals over side circuit No. 1 from east to west as well as transmission of such signals over side circuit No. 2 in both directions is accomplished in a manner similar to that described above.

In the absence of the bucking or neutralizing coil arrangement, which is the essence of the present invention, it has been found that passage of the direct current signals through the line windings of the repeating coils causes pulse distortion due to so-called cross-fire. Crossfire is a term commonly used by communication engineers when referring to interfering currents set up in one circuit, particularly a telegraph circuit, due to the passage of direct current signals through a paralleling circuit. The bucking orneutralizing coil arrangement of the present invention is effective in eliminating this trouble.

Referring again to the west terminal of side circuit No. 1 and assuming for the moment the absence of the bucking coils, it has been found that the direct current signals impressed on line I3 set up by induction, when passing through line winding II, currents in line winding I2 which, when uncorrected, result in signal distortion. With provision of the bucking coils, however, passage of the direct current signals through bucking or neutralizing coil H2 and line winding II set up voltages respectively in bucking coil H4 and line winding I2 by induction. (It will be understood that coils H2 and H4 have a common core and that line windings II and 12 have a common core.) Now, bucking coil H4 and line winding I2 are so poled with respect to one another that the voltages induced therein tend to neutralize each other, the net result being, therefore, that no disturbing voltages persist in line winding 12 due to the application of direct current signals to line I3.

In order that a more exact neutralization may be attained a closed conductive loop is provided which comprises inductance I6I and variable resistance I62 connected in series, inductance IGI being inductively associated with bucking coils H2 and H4. Variation of resistance I62 permits control of the coupling between coils H2 and H4 whereby the magnitude of the voltages induced in coil H4 by passage of direct current through coil H2 may be fixed at the exact desired value.

It will be understood that the arrangement functions in a similar manner with respect to direct current signals applied to line I4. In such instance passage of the direct current signals through bucking coil H4 and line winding I2 set up voltages by induction in bucking coil H2 and line winding II respectively. Bucking coil I I2 and line winding II are so poled with respect to each other that the induced voltages tend to neutralize one another.

It will be understood, further, that the bucking coil arrangements of the east terminal of side circuit No. 1 and those of the west and east terminals of side circuit No. 2 function in a manner similar to that described above.

Referring now to Fig. 2 there is illustrated the west terminal of a speech transmission system of the type utilizing combined line and hybrid coils. It will be understood that the arrangement of the east terminal will be similar to that of the west terminal illustrated and that one or more intermediate repeater sections may be included in the system. A complete system of this general nature is disclosed in the copending application of applicant and another referred to above.

Voice frequency currents impressed on lines I II and "2 by the speech transmitting equipment associated with side circuit No. 1 at the west terminal divide in the windings of hybrid coils I13, one-half of the energy passing into output path I'M of east-west amplifier I15 and being lost and the useful half passing into input path I76 of west-east amplifier I'II. After amplification these voice frequency currents again divide in the windings of hybrid coils IQI, one-half of the energy being absorbed by balancing network I92 and the useful half passing into lines I93 and IE4 for transmission to the east terminal or to the next intermediate repeater section. In view of the fact that the output path of west-east amplifier I'll and the input path of east-west amplifier H5 are coupled in conjugate relationship through the windings of hybrid coils ISI, no part of the amplified output of west-east amplifier III is fed back into the input path of eastwest amplifier I15.

Voice frequency currents are transmitted over side circuit No. 2 in a manner similar to that described above while voice frequency currents impressed on phantom line sections Eli! and 2M, after amplification by phantom west-east amplifier 283, are transmitted over a phantom circuit derived over lines 294 and 235. Line 204 ter- Inmates in side circuit No. I between capacitances 286 and 251' which are connected, in turn, across lines I93 and I94 While line 265 terminates in side circuit No. 2 between capacitances HI and 222 which are connected, in turn, across lines 223 and 223.

Direct current signals, for example telegraph signals, are applied to line I33 through retardation coil 225, bucking or neutralizing coil 226 and line windings 221 and 23I of hybrid coils I9I in series and are applied to line I9 3 through retardation coil 232, bucking coil 233 and line windings 234 and 235 of the hybrid coils in series. In this arrangement, as in the arrangement of Fig. 1 described above, it has been found that, in the absence of the bucking coil arrangement, passage of the direct current signals through the line windings causes pulse distortion due to so-called cross-fire. The bucking coil arrangement is effective in eliminating this trouble in the circuit of 2 in a manner similar to that described above in connection with Fig. 1. 7

Assuming for the moment the absence of the bucking coils, it has been found that the direct current signals impressed on line I33 set up by induction, when passing through line windings 221 and 23I, currents in line windings 23d and 235, which, when uncorrected, result in signal distortion. With the provision of the bucking coil arrangement, however, passage of the direct current signals through bucking coil 226 and line windings 221 and 23I set up voltages in buckin coil 233 and in line windings 234 and 235 respectively by induction. Bucking coil 233 is so poled with respect to line windings 234 and 235 that the voltages set up in the bucking coil neutralize those set up in the line windings, the net result being that no disturbing voltages persist in line windings 234 and 235 due to the application of the direct current signals to line I33.

As in the instance of the arrangement described above a closed conductive loop, comprising inductance 233 and variable resistance 23? connected in series, is provided to permit the attainment of a more exact neutralization.

t will be understood that the arrangement functions in a similar manner with respect to direct current signals applied to line I95. In such instance the direct current signals passing spectively. Bucking coil-226 is so poled withrespect to line windings 221 and 23I that the voltages induced in the line windings are neutralized by those induced in the bucking coil.

There is illustrated in Fig. 3 the intermediate repeater section of sidecircuit No. 1 of a system which is the same as that illustrated in Fig; 1 except for the fact that the bucking coil arrangement has been provided in the by-pass circuit also. In view of the fact that the system is otherwise as illustrated in Fig. l and described in detail above, it has not been considered necessary to illustrate the complete system and its operation will be described only in so far as action of the bucking coil arrangement in the by-pass circuit is concerned.

Direct current signals (telegraph) arriving at the intermediate repeater station of side circuit No. 1 over lines 25I and 252 pass respectively through line Winding 253 of repeating coil 253 and retardation coil 255 to line 255 and through line winding 251 of repeating coil 25 i and retardation coil ZISI to line 262. The direct current signals are by-passed around the intermediate repeater section over lines 256 and 62, and through bucking or neutralizing coils 283 and 28 3 and are reapplied to lines 263 and 26 through retardation coil 265 and line winding 266 of repeating coil 25? and through retardation coil 28I and line Winding 2 32 of repeating coil 23?,

respectively.

In the absence of the bucking coil arrangement of thepresent invention it has been found that signal distortion due to cross-fire has resulted from passage of the direct current signals through the line windings of the repeating coii. Assuming first the absence of the bucking coils, the direct current signals passing through line winding 253 of the repeating coil will set up disturbing voltages in line Winding 257 through inductance. With the provision of the bucking coil arrangement, however, direct current signals passing through line winding 253 and bucking or neutralizing coil 283 will set up voltages by induction in line winding 25'! and bucking coil 28d, respectively. Bucking coil 284 is so poled with respect to line winding 25'! that the voltages induced in the bucking coil neutralize those induced in the line winding, the net result being that no disturbing voltages persist in line winding 251 due to the passage of direct current signals through line winding 253.

As in the instance of the bucking coil arrangements described above a closed conductive loop, comprising inductance 235 and variable resistance 286 connected in series, is provided for the attainment of a more exact neutralization.

It will be understood that the bucking coil arrangement functions in a similar manner with respect to direct current signals passing through line winding 257. In such instance, the direct current signals passing through line winding 25 i and bucking coil 284 will set up voltages by induction in line winding 253 and bucking coil 233. Bucking coil 283 is so poled with respect to line winding 253 that the voltages induced in the bucking coil will neutralize those induced in the line winding, the net result being that no disturbing voltages persist in line winding 253 due to the passage of direct current signals through arrangement may be designed to also prevent the establishment of disturbing voltages in the line windings of repeating coil 26'! or that, if desirable, a separate set of bucking coils may be associated with that repeating coil.

W'hile certain specific embodiments of the invention have been selected for illustration and detailed description, the invention is not, of course, limited in its application to such embodiments. The embodiments described should be looked upon as illustrative of the invention and not as restrictive thereof.

What is claimed is:

1. In a speech transmission system, a terminal section, a two-wire line, a repeating coil for connecting said terminal section and said line, a composite set for transmission of direct current signals, the secondary of said repeating coil including two inductive winding portions of high impedance to voice frequencies and a portion of low impedance to voice frequencies but of high impedance to direct current, means for connecting the two legs of said composite set across said latter portion, means for neutralizing any disturbing effects set up in the windings of said repeating coil by passage therethrough of currents transmitted by said composite set, said neutralizing means including a winding connected in series with each leg of said composite set, said neutralizing windings being inductively coupled, and means for varying the closeness of the coupling of said neutralizing windings.

2. In a speech transmission system, a terminal section, a two-wire line, a repeating coil for connecting said terminal section and said line, a composite set for transmission of direct current signals, the secondary of said repeating coil including two inductive winding portions of high impedance to voice frequencies and a portion of low impedance to voice frequencies but of high impedance to direct current, means for connecting the two legs of said composite set across said latter portion, means for neutralizing any disturbing efiects set up in the windings of said repeating coil by passage therethrough of currents transmitted by said composite set, said neutralizing means including a neutralizing winding connected in series with each leg of said composite set, said neutralizing windings being inductively coupled, and means for varying the closeness of the coupling of said neutralizing windings, said last-mentioned means including a closed conductive loop comprising a winding and a variable resistance connected in series, said last-mentioned winding being inductively coupled to said neutralizing windings.

3. In a speech transmission system, a west terminal, an east terminal, and a two-wire line for connecting said west and said east terminals, a

'two-way repeater for voice frequencies at said west terminal, a, hybrid coil and balancing network at said west terminal for connecting said line to two sides of said repeater in mutually conjugate relationship, a line winding of said hybrid coil being connected in series with each side of said two-wire line, means at said west terminal for applying direct current signals to each side of said two-wire line in series respectively with said line windings of said hybrid coil, means for neutralizing disturbing efi'e-cts induced in one of said line windings by passage of direct current signals through the other of said line windings, said means comprising a neutralizing winding connected in series with each side of said two-wire line between the respective line windings and the respective points of application of the direct current signals, said neutralizing windings being inductively coupled, and means for varying the closeness of the coupling of said neutralizing windings.

4. In a speech transmission system, a west terminal, an east terminal, and a two-wire line for connecting said west and said east terminals, a two-way repeater for voice frequencies at said west terminal, a hybrid coil and balancing network at said west terminal for connecting said line to two sides of said repeater in mutually conjugate relationship, a line winding of said hybrid coil being connected in series with each side of said two-wire line, means at said west terminal for applying direct current signals to each side of said two-wire line in series respectively with said line windings of said hybrid coil, means for neutralizing disturbing effects induced in one of said line windings by passage of direct current signals through the other of said line windings, said means comprising a, neutralizing winding connected in series with each side of said two-wire line between the respective line windings and the respective points of application of the direct current signals, said neutralizing windings being inductively coupled, and means for varying the closeness of the coupling of said neutralizing windings, said last-mentioned means including a closed conductive loop comprising a winding and a variable resistance connected in series, said last-mentioned winding being inductively coupled to said neutralizing windings.

5. In a speech transmission system, a west terminal, an intermediate repeater section, an east terminal, a first two-wire line for connecting said west terminal and said intermediate section, a second two-wire line for connecting said intermediate section and said east terminal, means at said west terminal for applying voice frequency currents to said first two-wire line, means at said west terminal for applying direct current signals to both sides of said first two-wire line, a twoway repeater for voice frequency currents at said intermediate repeater section, conductive means connected across the intermediate repeater section end of each of said two-wire lines, each of said conductive means comprising two portions of high impedance to voice frequencies connected by a portion of low impedance to voice frequencies but of high impedance to direct currents, a by-pass path at said intermediate repeater section for by-passing direct current signals from said first two-wire line around said two-way repeater to said second two-wire line, said by-pass path comprising two lines and being connected across said respective portions of low impedance to voice frequencies of said conductive means, means in said by-pass path for neutralizing any disturbing effects that may be set up in one part of the direct current path by passage of direct current signals through another part of the direct current path, said neutralizing means comprising a neutralizing winding connected in series with each of said lines of said by-pass path, said neutralizing windings being inductively coupled, and means for varying the closeness of the coupling of said neutralizing windings.

6. In a speech transmission system, a west terminal, an intermediate repeater section, an east terminal, a first two-wire line for connecting said west terminal and said intermediate section, a second two-wire line for connecting said intermediate section and said east terminal, means at said west terminal for applying direct current signals to both sides of said first two-wire line, a two-way repeater for voice frequency currents at said intermediate repeater section, conductive means connected across the intermediate repeater section end of each of said two-wire lines, each of said conductive means comprising two portions of high impedance to voice frequencies connected by a portion of low impedance to voice frequencies but of high impedance to direct currents, a bypass path at said intermediate repeater section for by-passing direct current signals from said first two-wire line around said two-way repeater to said second two-wire line, said by-pass path comprising two lines and being connected across said respective portions of low impedance to voice frequencies of said conductive means, means in said bypass path for neutralizing any disturbing effects that may be set up in one part of the direct current path by passage of direct current signals through another part of the direct current path, said neutralizing means comprising a neutralizing winding connected in series with each of said lines of said by-pass path, said neutralizing windings being inductively coupled, and means for varying the closeness of the coupling of said neutralizing windings, said last-mentioned means including a closed conductive loop comprising a winding and a variable resistance connected in series, said lastmentioned winding being inductively coupled to said neutralizing windings.

7. In a speech transmission system, a terminal section, a repeater section, a two-wire line for connecting said terminal section and said repeater section, a composite set for transmission of direct current signals, said composite set including two conductive legs, conductive means connected across the terminal section end of said two-wire line, said conductive means comprising a first inductance, a capacitance and a second inductance connected in series in the order named, means for connecting one of said legs of the composite set to said conductive means at the junction of said first inductance and said capacitance, means for connecting the other of said legs of the composite set to said conductive means at the junction of said capacitance and said second inductance whereby direct current signals transmitted over the first leg will pass through said first inductance to one side of said two-wire line and direct current signals transmitted over the second leg will pass through said second inductance to the other side of said two-wire line, and means included in said composite set for neutralizing any disturbing efiects set up in one of said inductances by passage of direct current signals through the other of said inductances.

8. In a speech transmission system, a terminal section, a repeater section, a two-wire line for connecting said terminal section and said repeater section, a composite set for transmission of direct current signals, said composite set including two conductive legs, conductive means connected across the terminal section end of said two-wire line, said conductive means comprising a first inductance, a capacitance and a second inductance connected in series in the order named, means for connecting one of said legs of the composite set to said conductive means at the junction of said first inductance and said capacitance and means for connecting the other of said legs of the composite set to said conductive means at the junction of said capacitance and said second inductance whereby direct current signals transmitted over the first leg will pass through said first inductance to one side of said two-wire line and direct current signals transmitted over the second leg will pass through said second inductance to the other side of said two-wire line, means included in said composite set for neutralizing any disturbing efiects set up in one of said inductances by passage of direct current signals through the other of said inductances, said neutralizing means including a neutralizing winding connected in series with each leg of said composite set, said neutralizing windings being inductively coupled, and means for varying the closeness of the coupling of said neutralizing windings.

9. In a speech transmission system, a terminal section, a repeater section, a two-wire line for connection said terminal section and said repeater section, a composite set for transmission of direct current signals, said composite set including two conductive legs, conductive means connected across the terminal section end of said two-wire line, said conductive means comprising a first inductance, a capacitance and a second inductance connected in series in the order named, means for connecting one of said legs of the composite set to said conductive means at the junction of said first inductance and said capacitance and means for connecting the other of said legs of the composite set to said conductive means at the junction of said capacitance and said second inductance whereby direct current signals transmitted over the first leg will pass through said first inductance to one side of said two-wire line and direct current signals transmitted over the second leg will pass through said second inductance to the other side of said two-wire line, means included in said composite set for neutralizing any disturbing effects set up in one of said inductances by passage of direct current signals through the other of said inductances, said neutralizing means including a neutralizing winding connected in series with each leg of said composite set, said neutralizing windings being inductively coupled, and means for varying the closeness of the coupling of said neutralizing windings, said lastmentioned means including a closed conductive loop comprising a winding and a variable resistance connected in series, said last-mentioned winding being inductively coupled to said neutralizing windings.

EDMUND R. TAYLOR. 

